1. Field of Invention
This invention relates to instrumentation and particularly to instrumentation in an environment requiring accurate and continuous extraction of test data during system operation. A particular application of this invention is a time delay for control and monitoring functions in an operating nuclear power plant. The invention has other applications where continuous testing and fail-safe operation are requisites.
2. Description of the Prior Art
Time delay devices are relatively well-known to the instrumentation art. Testable time delay devices are also known, all known test procedures are in some way disruptive of normal functional operation. Thus some defects in a time delay device may go undetected until on-line failure occurs. No time delay device is known which is capable of being tested at any time and specifically at any time during normal operation. Consequently extensive manual labor is now expended in frequent off-line testing of such devices.
What is needed is a time delay which is testable during its operation, and specifically a time delay device which is self testable in a manner which does not in any way disrupt normal functional operation of the device.